Failures of conventional separable electrical contacts can be classified as both short and long term. Two short term failure modes are contact stubbing and over stressing of the contact tynes. Stubbing occurs when the insertion force of the male portion coupled with misalignment of the male portion upon insertion into the female portion damages one or more of the tynes as well as the lead-in section of the female portion. Over stressing results in substantial reduction in contact normal force. The reduction in contact force causes high contact resistance which can lead to over heating and burnt contacts when the current level is high.
Two long term failure modes are stress relaxation of the contact tynes and fretting. The relaxation of the contacts can be mitigated by providing additional mechanical assist or lowering the stress levels in the contact tynes. However, due to packaging and contact physics requirements, it is very difficult to eliminate relaxation of the contacts altogether. Fretting is the relative micro-motion at the contact interface between male and female contact portions. There are typically three fretting failure modes. The first two modes, known as rocking and twisting, are female contact portion angular displacement relative to the longitudinal axis of the male contact portion. The third failure mode, known as sliding, is the translational motion of the contact portions relative to one another. Fretting causes the interface between the male and female contact portions to wear out. Thus causing high contact resistance which in turn exhibits the same type of failure as previously described for short term failure modes.
Electrical contact design efforts have been directed at solving the aforementioned problems. One design of an electrical contact is disclosed in U.S. Pat. No. 4,545,638 entitled Rib Cage Terminal. The female connector disclosed therein has a central spine from which extends, at first and second ends of the connector, one or more pairs of cantilevered beams. The beams in each pair are angled forwardly or rearwardly and are formed into a structure generally reminiscent of a human rib cage. The ribbed structure defines a generally enclosed opening. The connector is received in a cavity formed in a housing. The housing is utilized for structural rigidity because the disclosed "rib cage" connector is not robust enough to operate as a stand alone connector.
This design is disadvantageous because the extra step of placing the connector in a housing increases manufacturing difficulty and adds cost. Further, this operation is often done by hand and is therefore prone to human error. For example, due to the repetitive nature of the operation it is common for the operator to "miss" placing a connector in a particular housing. This housing, when used in the field, will have to be discarded.
Accordingly, a need exists in the art for an electrical connector which overcomes long and short term failure modes, is robust enough to withstand repeated use, and lacks the manufacturing difficulty, cost and error associated with previous designs.